A compound of the structural formula (I) and a compound of the structural formula (II) are known compounds. It is known that the compound of the structural formula (II) can be prepared by subjecting a compound of the structural formula (III) or (E)-1-benzyl-4-[(5,6-dimethoxy-1-indanon)-2-ylidene]methylpiperidine to a hydrogenation reaction. It is also known that the compound of the structural formula (I) can be prepared by treating the compound of the structural formula (II) with hydrochloric acid (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3).
Patent Document 1: JP-A-1-79151
Patent Document 2: Japanese Patent No. 2578475
Patent Document 3: JP-A-4-187674
Patent Document 1 discloses a reaction formula as shown below (page 15, lower right column, line 2 to page 16, upper left column, line 1 of the specification).

That is, Patent Document 1 discloses a process for preparing a compound of the formula (B) by reducing a compound of the formula (A) that contains a compound in which J1 is indanone, and describes that “when carrying out catalytic reduction, use of, for example, palladium carbon, Raney nickel, rhodium carbon, or the like as a catalyst leads to a favorable result” (page 16, upper left column, lines 11 to 13 of the specification). Moreover, as a process for preparing donepezil hydrochloride using donepezil as a raw material, a concentrated residue of the compound of the structural formula (II) is dissolved in methylene chloride, and the mixture is treated with 10% hydrochloric acid-ethyl acetate is exemplified (Example 4).
However, Patent Document 1 shows examples of a catalyst to be used in catalytic reduction such as palladium carbon, Raney nickel, rhodium carbon, but does not mention any specific catalytic reduction process. Patent Document 1 only discloses a production example (Example 1) that uses 5% rhodium-carbon as a catalyst, and a production example (Example 4) that uses 10% palladium-carbon as a catalyst. There is no disclosure about a catalytic reduction process using Raney nickel as a catalyst.
Patent Document 2 discloses a reaction formula as shown below (page 3, lines 6 to 8 of the specification).

That is, Patent Document 2 discloses a process for preparing a compound of the formula (D) that is a desired substance obtained by catalytically reducing a compound of the formula (C), and describes that “when carrying out catalytic reduction, use of, for example, palladium carbon, Raney nickel, rhodium carbon, or the like as a catalyst leads to a favorable result” (page 3, lower right column, line 6 to line 4 from the bottom of the specification). As a process for preparing donepezil hydrochloride using donepezil as a raw material, a concentrated residue of donepezil is dissolved in methylene chloride, and the mixture is treated with 10% hydrochloric acid-ethyl acetate is exemplified (Production Example 1).
However, Patent Document 2 shows examples of a catalyst to be used in catalytic reduction such as palladium carbon, Raney nickel, rhodium carbon, but does not mention any specific catalytic reduction process. Patent Document 2 discloses a production example that uses 10% palladium-carbon as a catalyst in Production Example 1. There is no disclosure about a catalytic reduction process using Raney nickel as a catalyst.
Patent Document 3 discloses a reaction formula as shown below (page 4, lines 1 to 2 of the specification).

That is, Patent Document 3 discloses a process for preparing an optically active compound of the formula (D) by asymmetrically hydrogenating (E)-1-benzyl-4-[(5,6-dimethoxy-1-indanon)-2-ylidene]methylpiperidine represented by the formula (E) in the presence of an optically active ruthenium-phosphine complex catalyst.
In the process of the compound of the structural formula (II) by catalytic hydrogenation in Patent Document 1 and Patent Document 2, a compound of the structural formula (F)
is likely to be prepared as a by-product in the catalytic hydrogenation reaction. Therefore, known purification means such as column purification or recrystallization is needed for subjecting the compound of the structural formula (II) to the next reaction. Specifically, catalytic hydrogenation is carried out using 10% palladium-carbon as a catalyst at room temperature and atmospheric pressure for 6 hours, and then a purification step is carried out. That is, following steps are necessary after catalytic hydrogenation: filtering out the catalyst from the reaction solution, distilling off the solvent, purifying the obtained residue by silica gel column chromatography, and concentrating the eluted fraction. However, this process has various problems such as decreasing the yield, and increasing the number of purification operations, and therefore cannot be said to be sufficient as a process for industrially producing the compound of the structural formula (II).
In Patent Document 1 and Patent Document 2, these purification steps aim to remove the above described impurities. However, there is a need for a process for preparing the compound of the structural formula (I) and the compound of the structural formula (II), in which the amount of impurities are decreased more, and which is easily operated and suitable for industrial production.